Core A is organized to meet demonstrated statistical needs of participating scientists in the areas of biostatistical design and analysis, and data management. Please see the Appendix for additional descriptions of biostatistical methodology. The objectives of Core A are as follows: 1. To assist in the biostatistical design of clinical and laboratory studies in this Program Project Grant (PPG). 2. To assist in the analysis of research data. In this role, the core provides assistance to multiple investigators in implementing study protocol design, data entry, data monitoring and analysis and manuscript w r i t i n g . 3. To provide experienced staff to carry out analyses. 4. To assist investigators in all aspects of data management including the organization of their data flow and in the choice and setup of data base management systems. 5. To develop biostatistical methodology for statistical problems arising in this PPG. 6: To provide scientific input more generally as a member of the Executive Committee.